Underground farms could use redundant tunnels and fix carbon dioxide

Abandoned mines could be reused as underground farms to grow crops under cities while absorbing carbon dioxide from the atmosphere, according to Nottingham University researchers

Looking down the shaft of a vertical underground farm

Many regions around the world are riddled with tunnels that are no longer in use. Coalmines whose reserves have been depleted; civic air defence infrastructure from more troubled times; many are currently lying abandoned, and are often underneath land which cannot be used for cultivation, such as cities. Researchers from Nottingham University are about to embark on a research project to determine how such tunnels could be reused as underground farms, both providing space to grow crops and forming a sink to absorb carbon dioxide.

Civil engineers around the world have in recent years become interested in underground building techniques, trying to solve the problem of increasing populations by building downwards rather than upwards. However, most of the effort has looked at residential, retail or commercial space rather than considering agriculture.

Prof Saffa Riffat, chair in sustainable energy at Nottingham’s faculty of engineering, is working with research fellow Prof Yijun Yuan, a specialist in mining engineering and sustainable energy, on the two-to-three year project, which will focus on opportunities in the UK and China.

“In the UK there are over 1,500 redundant coal mines, and in China, there are over 12,000 abandoned coal mines (0.6 million m3), 7.2 billion m3 of tunnels and about one billion m3 of civic air defence tunnels,” said Prof Riffat.

Such facilities would of course need artificial lighting, and also a source of nutrients for the plants. The researchers envisage using hydroponic or even aeroponic systems, growing the plants in nutrient-rich water or a mist environment, and lighting the tunnels using LEDs selected to provide the optimum light wavelengths to meet the plants’ needs for photosynthesis in the absence of sunlight. Harvesting would be fully automated, using advanced robotic systems which could also handle planting.

Crops in underground farms could be grown using aeroponics, spraying the plants with a nutrient-rich mist

Groundwater could be used directly in these farms or water could be condensed from ambient air (coalmines in particular are often humid environments). The researchers are also designing advanced control systems including sensors and remote controls to monitor the health of the crops and adjust conditions to optimise growth and yields. These, along with the necessary pumps and lighting, would be powered by renewable energy or run on an off-peak electricity tariff.

One major advantage of growing crops in such artificial conditions is that they are no longer dependent on natural variations of the weather cycle or seasonality, allowing them to be produced all year round. It would also potentially allow them to be grown in arid or water-deficient conditions, as well as in cold climates and regions which do not receive regular or reliable sunlight.

Fully-automated underground farms could use robots for planting and harvesting

“Many crops are now being grown in greenhouses. Although this provides a controllable growth environment, greenhouses are heavy energy consumers,” said Prof Riffat. “Vertical farms are a relatively recent adaptation of the traditional greenhouse and are suitable for use in cities, as their tall glass structures provide high crop yields on a small land area.

“However, vertical farming systems are expensive to manufacture and install, and require a large amount of water and energy for heating and cooling. They are also vulnerable to extreme weather conditions, wars and terrorism.”

The project will also investigate connecting the existing redundant tunnels with new networks, which could be drilled using automated equipment or made by controlled explosion.

The Nottingham team has obtained a patent for the techniques, including the construction of deep vertical shafts to house farms, which could then be connected to existing tunnel networks.

This sounds like a fun project to be involved in.
Have they decided what level of Co2 they will be pumping into the underground farms to achieve maximum growth potential? Greenhouse production is enhanced by elevated Co2 it is essential for photosynthesis and provides multiples of yield when above 1000 PPM compared to the background ambient 410 PPM.

The atmosphere in a coal mine is usually rich in CO2 anyway so there should be no need to add any more. The important issue is that unless the electricity used to provide the lighting is carbon free there will be a net gain in CO2 emissions.

Pretty insane, considering the heat units from growing in the open – this would make sense in a survival bunker or an offworld colony, so it might be worth diverting some power and resources for experimental purposes.

It is good to see that the penny has (slowly) dropped in that the idea of underground agriculture should be taken seriously in the light of climate change. What is needed is massive investment in which most of this kind of thing can be undertaken on a huge scale…Such funding could come about with the development of a New Paradigm

This sort of article should really be kept for April Fool’s day. If anyone wants the exhaustive list of reasons this will never be economically viable for anything other than a vanity trip to Mars I am happy to follow up.